1) Field of the Invention:
This invention relates to a retractor with a means for detecting the amount of a wound webbing, said retractor being suitable for use in a seat belt system for protecting an occupant in the event of a vehicular emergency, and especially to a retractor capable of detecting a released, i.e., unlatched state of an emergency release buckle on the basis of the amount of a wound webbing.
2) Description of the Related Art:
Webbing retractors have conventionally been provided with an unlatched buckle warning device to detect unlatching of a tongue, which is fastened to one end of an associated webbing, from the corresponding emergency release buckle.
In the above unlatched buckle warning device, detection of tongue unlatching from the emergency release buckle has generally been conducted on the basis of the amount of the webbing wound in the retractor. Known means for the detection of the amount of a wound webbing include those relying upon the diameter of a webbing wound on an associated retractor shaft, said diameter varying depending on the amount of the webbing wound on the retractor shaft, and those making use of the number of revolutions of a retractor shaft which has taken up an associated webbing.
The former means are accompanied by a drawback that they are not fully reliable in the accuracy of detection, because the webbing may not be wound in the form of a true circle on the retractor shaft and the diameter of the wound webbing changes as little as the thickness (1.0-1.5 mm) of the webbing per revolution of the retractor shaft.
On the other hand, the latter means require to conduct detection after significant reduction of the number of revolutions of the retractor shaft of the webbing retractor, since the retractor shaft undergoes as many as 10-20 revolutions. Combining of conventional gears for the significant reduction of the number of revolutions of the retractor shaft has however led to need for more gears and a smaller module. This has in turn resulted in a more complex structure and also in a strength reduction.
Because of the significant reduction of the number of revolutions of the retractor shaft, the accuracy of detection is substantially affected by any error in the position of a detector, leading to another drawback that the latter means are not fully reliable in the accuracy of detection.